(a) Explain the following terms: (i) test cross (ii) monohybrid cross. (b) In a mango plant the, the allele for bean-shaped seed is r and is recessive to ro...

(a)(i) Test cross: This is the crossing of an organism showing a dominant character, but whose genotype is unknown, with a homozygous recessive organism in order to determine the unknown genotype.

(a)(ii) Monohybrid cross: This is a genetic cross involving one pair of contrasting alleles, used to study the inheritance of a single character.

(b) Let R represent the allele for round-shaped seed (dominant) and r represent the allele for bean-shaped seed (recessive).

(i) Homozygous bean-shaped parent × homozygous round-shaped parent

Parental genotypes: \(rr \times RR\)

All the offspring have genotype \(Rr\). Therefore, all the offspring are round-shaped.

Genotypic ratio: 100% \(Rr\)

Phenotypic ratio: 100% round-shaped seeds.

(ii) Heterozygous cross

A bean-shaped plant cannot be heterozygous because the heterozygous genotype \(Rr\) produces round-shaped seeds. Thus, the stated heterozygous parents have genotype \(Rr\), and the genetic cross is \(Rr \times Rr\).

Offspring genotypes are \(RR, Rr, Rr\), and \(rr\).

Genotypic ratio: \(1RR : 2Rr : 1rr\).

Phenotypic ratio: \(3\) round-shaped seeds : \(1\) bean-shaped seed.